A special dye used as color former for heat sensitive recording paper or pressure-sensitive carbon paper is called heat and pressure sensitive dyes. With the development of science and technology, especially the modernization of scientific and technological information and the widespread use of computers and fax machines, the amount of heat sensitive recording paper and pressure sensitive carbon paper is increasing. Therefore, more and more attention has been paid to the research and development of heat and pressure sensitive dyes.
- Pressure-sensitive carbon paper: Pressure-sensitive carbon paper is composed of pressure-sensitive dyes, solvents, chromogenic agents and capsule membrane materials, among which pressure-sensitive dyes are an important part of pressure-sensitive carbon paper. Among them, the pressure-sensitive dyes are dissolved in non-volatile solvent, and then wrapped with the thin capsule membrane to become tiny particles with a few microns in diameter. When subjected to pen pressure or typing pressure, the microcapsule film ruptures, and the pressure-sensitive dye solution is transferred and absorbed into the chromogenic layer to display the color. This pressure-sensitive carbon paper is mainly used for pulse recording, and is widely used as fax carbon paper.
- Heat sensitive recording paper: Heat sensitive dyes are mainly used for heat sensitive recording paper. When subjected to hot pen or hot head, dye and solid acid will melt and react, resulting in color. This recording method has the characteristics of no noise and odor, simple operation and low price. With the development of fax, the performance of heat sensitive dyes will be further improved.
- Phthalein heat-sensitive and pressure-sensitive dyes: Phthalein heat and pressure sensitive dyes are the earliest researched systems, including PH-1, PH-3 and others. PH-1 (Crystal Violet Lactone, CVL) gives off a bright, high-concentration cobalt blue by cracking the lactone ring. This kind dyes have the advantages of fast color development, good solubility, no sublimation, high color concentration and low price. PH-3 is another important heat and pressure sensitive dye that shows red color, which has the advantages of high color concentration and good light resistance. Due to acid sensitivity, PH-3 cannot be used on acid paper.
Figure 1. Molecular structure of PH-1.
- Fluorane heat and pressure-sensitive dyes: Fluorane heat and pressure-sensitive dyes are characterized by a complete spectrum, in particular the ability to produce a pure black color. In addition, the color concentration of fluorane heat and pressure sensitive dyes is not high, but the light resistance, water resistance and chemical resistance are good. Among them, F-6 is an excellent dye, which can obtain a stable black color when using resins as chromogenic agent.
Figure 2. Molecular structure of F-6.
- Phenothiazine and phenothiazine heat and pressure-sensitive dyes: Using carclazyte as chromogenic agent, phenothiazine and phenothiazine heat and pressure sensitive dyes can show blue or green color. Although the dyeing speed is very slow, it has good light resistance after dyeing. Therefore, it can be mixed with CVL to obtain dyes with excellent performance.
Figure 3. Molecular structure of phenothiazine heat and pressure sensitive dye.
- The others: In addition to the mentioned above, there are many other types, an example of those is shown in Figure 4.
Figure 4. An example of other heat and pressure sensitive dye.